1. Field of the Invention
This invention relates to a semiconductor device including a semiconductor chip covered with a protective sheet, and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, a semiconductor physical quantity sensor such as a semiconductor acceleration sensor or a semiconductor pressure sensor includes a movable part formed on a silicon chip. Such a sensor outputs an electrical signal corresponding to a physical quantity such as acceleration or pressure, according to a displacement of the movable part.
For instance, JP-A-9-211022 discloses an acceleration sensor including a beam structure that is formed on a silicon substrate as a movable part and is displaced upon receiving an acceleration, a. movable electrode disposed on the beam structure, and a fixed electrode formed on the silicon substrate to face the movable electrode. The accelerating sensor detects acceleration based on a change in distance between the movable electrode and the fixed electrode.
This kind of semiconductor device usually includes a protective cap for covering and protecting the movable part. As disclosed in JP-A-6-347475, a glass substrate, which is bonded to a semiconductor wafer by anode coupling, can be used as the protective cap. In this case, however, the glass substrate is liable to form gaps at the bonding portion with the semiconductor wafer due to surface roughness of its bonding interface. Therefore, when dicing cut is carried out, grinding water easily enters into the semiconductor device through the gaps to cause various problems. For instance, the water may disturb the movement of the movable part due to surface tension thereof.
On the other hand, JP-A-9-27466 discloses not a glass substrate but an UV-hardening sheet as a protective cap. When the UV-hardening sheet is used as the protective cap, the problem such that grinding water enters into the semiconductor device during the dicing cut does not occur. However, the UV-hardening sheet is deformed at a temperature of approximately 8.degree. C. to 90.degree. C. Because of this, the UV-hardening sheet must be detached from the semiconductor device when subsequent steps such as a wire bonding step necessitating a temperature higher than that are carried out. This results in an increase in a number of manufacturing steps.
Further, there is a both-surface exposed type structure including a beam structure (movable part) as a sensing part that is exposed on both surfaces of a chip. In such a structure, when the chip is mounted on a lead frame by adhesive, or is fixed to a package by adhesive, the adhesive is liable to contact the sensing part to disturb the movement of the movable part. When the both-surface exposed type sensor chip is molded with resin, the resin easily contacts the movable part. Even when the sensor chip is fixed to the lead frame or the package, the resin can contact the movable part by passing through a gap at the bonding portion of the chip.